This invention relates generally to the field of ink jet printing, and more particularly to mailing machines which incorporate ink jet technology and have the capability of printing postage indicia either on envelopes fed successively through the mailing machine or on discrete lengths of tape that is stored in and dispensed from the mailing machine and then manually affixed to bulky mail pieces or packages.
Automatic high speed mailing machines of the type with which the present invention is utilized have long been well known and have achieved a high degree of commercial success. Mailing machines of this type typically include an elongated feed deck, an envelope conveyor mechanism extending along the feed deck, a hopper for holding a stack of envelopes with the flaps still open, a flap closing and sealing device located just downstream from the hopper, and a postage meter mounted over the feed deck just downstream from the flap closing and sealing device. The postage meter typically includes an accounting device for monitoring the amount of postage dispensed and a printing device for printing a postage indicia on the envelopes as they are fed along the feed deck. The postage meter further includes a postage amount setting mechanism by which the postage meter is manually set to print an appropriate amount of postage as required by the weight of the envelopes being fed through the mailing machine. Some of the more sophisticated mailing machines include an envelope weighing device interposed between the flap closing and sealing device for weighing each envelope as it passes over the weighing device and the postage meter for automatically setting the postage to print an appropriate amount of postage in the postage indicia.
Traditionally, from the earliest development of postage meters, the printing devices therein have utilized ink transfer technology, in which ink is transferred from a storage device to a rotary or flat bed printing die of the printing device, and the ink then being transferred from the printing die to the envelope, either by rotation of a curved printing die while the envelope is in motion, or by suitably pressing the envelope against the flat bed printing die. However, recent technological advances in the field of ink jet technology have resulted in this form of printing technology being adopted for use in postage meters, with the result that the printing devices in postage meters can now provide the same technical and operator advantages as are offered by ink jet technology in other types of printing applications.
One of the most significant problems that had to be overcome in adapting postage meters for use with ink jet technology was that of establishing and maintaining a proper physical orientation between the surface of an envelope traveling through the mailing machine on which the postage indicia was to be printed or between the surface of a piece of tape stored in the mailing machine on which the postage indicia was to be printed. In all prior mailing machines which utilized ink transfer technology, both the envelopes and the tape on which the postage indicia was printed were supported by a fixed surface against which the rotary or flat bed printing die pressed the envelope or piece of tape in order to effectively transfer the ink from the die to the surface of the envelope or tape. It must be remembered that a postage meter, in effect, is printing an indicia that is the equivalent of money, and therefore the print quality of the indicia must meet certain minimum standards for this type of printing established by the local Postal Authority. It was therefore critical that an effective and reliable die to envelope or tape surface pressure contact be obtained for each printing operation to ensure that the required printing quality was obtained. This presented little problem with the prior arrangement of providing a printing die which pressed against a printing surface which in turn was rigidly supported by a fixed surface during the printing operation.
All of this changed with the advent of ink jet technology in the postage meter field. In order for the ink jet nozzles of any ink jet printer to deposit ink on the surface of a receiving medium, it is critical that a small predetermined gap be maintained between the exit plane of the nozzles and the surface of the receiving medium, typically in the order of one sixteenth to one thirty-second of an inch. This gap is necessary to achieve proper and acceptable image quality, since too small a gap causes excessive ink to be deposited in the actual image area, resulting in a poor image quality, and too large a gap results in an image that appears fuzzy or out of focus. In heretofore conventional printing devices utilizing ink jet technology, such as computer printers, maintaining this gap was not a problem because the sheet of paper on which printing was taking place was always supported on a rigid, stationary surface while printing is taking place. For example, in a typical printer, the sheet of paper is typically wrapped partly around a roller and the ink jet print head moves laterally across the sheet to produce a line of print. When a full line has been printed, the sheet is indexed to the next line, and the print head moves across the sheet to print a second line, and so on until the printing operation is complete. In addition, in conventional ink jet printers, the item being printed upon does not vary in thickness so that, as long as the sheet remains flat on the supporting surface, there will be no variation in the gap between the printing surface and the plane of the ink jet nozzles. Also, conventional printers utilize a motor to drive the roll and then feed the tape web across the print means. The orientation of the motor connected to the roll employs a larger motor such that the inertia of the roll can be overcome. However, these large motors are expensive and, due to the large force, may tear or inconsistently feed the tape web.
The problem of maintaining the critical gap between the surface of an envelope and the plane of the ink jet nozzles was effectively solved with the invention disclosed and claimed in U.S. patent application Ser. No. 08/951,073 filed on Oct. 15, 1997 now U.S. Pat. No. 5,923,343 entitled MAILING MACHINE HAVING REGISTRATION SHIELD FOR INK JET PRINTING ON ENVELOPES and assigned to the assignee of this application. However, the invention disclosed and claimed in that application did not solve the problems inherent in utilizing ink jet technology in a postage meter to print a postage indicia on a discrete length of tape stored in the mailing machine. Since the thickness of the tape does not vary as it does with envelopes, the top registration invention of the prior application was not applicable to printing on tape. Also, once printing occurs on the envelope, it is ejected from the mailing machine and the next envelope is immediately presented to the printing device. With tape, on the other hand, when printing takes place on a discrete portion of the tape, which is typically stored in roll form and fed as a web, the tape must be advanced to a position where the printed portion can be severed from the web and ejected from the mailing machine, after which the tape must be fed in a reverse direction to bring the new leading edge of the web to the printing position, thereby avoiding what would otherwise be an unacceptable degree of waste of tape each time an indicia is printed. Still further, since the printed postage indicia is relatively small in relation to the surface area of an envelope, there is ample surface area available for engagement with the envelope of various types of feeding mechanisms to move the envelope through the mailing machine after printing occurs without running the risk of smearing the ink within the postage indicia area by contact with any part of the feeding mechanisms. With the tape, on the other hand, the size of the postage indicia is such that it occupies a major portion of the height of the strip of tape, thereby leaving very little marginal portion of the tape for contact with any portion of a tape feeding mechanism for moving the tape forwardly for printing and severing and then backwards to realign the new leading edge of the tape with the beginning of a printing location. Finally, it has been found that mailing machines of the type with which ink jet technology is utilized for printing postage indicia on envelopes can operate at such a high rate of speed that typical tape storing and feeding mechanisms cannot operate successfully to commence feeding of the tape without running a high risk of tearing it, simply because the stored roll of tape cannot be accelerated fast enough to reduce the shock of the sudden acceleration on the tape, with the result that the tape frequently tears, and the mailing machine must be shut down to rethread the tape through the feeding mechanism.
Thus, despite the successful solutions to the problems of printing postage indicia on envelopes using ink jet technology, several significant problems remain in printing postage indicia on tape for later affixation to bulky envelopes and packages. And since this capability is an important contribution to the commercial acceptance of large, high volume mailing machine, there remains a critical need for the development of an effective mechanism for storing and feeding tape in a mailing machine on which postage indicia can be printed with the same degree of speed and acceptable print quality that has been achieved in connection with printing of envelopes.